The companies have been in negotiations since February and signed a confidentiality accord, said the people, who declined to be identified because the information is private. Talks between Gem and Lucara, valued at about $606 million and $412 million respectively, may not lead to a deal, the people said.

Sophia Shane, a spokeswoman for Lucara in Vancouver, said March 18 she wasn’t aware of any talks or confidentiality accord.

Gem has advanced 7 percent to 270 pence on the London Stock Exchange this year, while Lucara has risen 18 percent to C$1.12 in Canadian trading. The Bloomberg World Mining Index has declined 7 percent.

Gem, based in London, operates the Letseng mine in Lesotho and is developing a new mine in Botswana. Lucara has a diamond project adjacent to Letseng, called Mothae, as well as operations in Botswana and Namibia.